1. Field of Invention
Embodiments of the present invention relate generally to chemical compounds, semiconductor devices fabricated using such chemical compounds and methods of forming such semiconductor devices. More particularly, embodiments of the present invention relate to a germanium compound, a semiconductor device fabricated using the germanium compound and methods of fabricating such a semiconductor device.
2. Description of the Related Art
Volatile memory devices and nonvolatile memory devices are types of semiconductor devices. Data stored within volatile memory devices is lost when power is not supplied to the memory device. However, nonvolatile memory devices retain stored data even in the absence of power. Accordingly, nonvolatile memory devices have been widely used in memory cards, telecommunication systems and the like.
Nonvolatile memory devices include flash memory devices or phase change memory devices. Phase change memory devices are very attractive as next-generation memory devices to replace flash memory devices. Phase change memory devices typically include a phase change material that may exhibit one of at least two different phases—for example a crystalline phase and an amorphous phase. The phase of the phase change material may be changed into an amorphous phase or a crystalline phase according to a heating temperature applied thereto and a quenching process of the heated phase change material. The phase change material having the crystalline phase exhibits a relatively low electrical resistance and phase change material having the amorphous phase exhibits a relatively high electrical resistance.
FIG. 1 is a cross sectional view illustrating a fabrication method of a conventional phase change memory device.
Referring to FIG. 1, an insulating layer 30 is formed on a substrate 10 having a lower interconnection 20. The insulating layer 30 is patterned to form an opening 35 and a lower electrode 40 is formed in the opening 35. A phase change material layer and an upper electrode layer are sequentially formed on the lower electrode 40 and the insulating layer 30. Each of the phase change material layer and the upper electrode layer may be formed using a physical vapor deposition technique such as a sputtering method. The upper electrode layer and the phase change material layer are then patterned using a conventional photolithography process and a conventional etching process to form a phase change material pattern 50 and an upper electrode 60, which are sequentially stacked on the lower electrode 40.
As phase change memory devices become more highly integrated, the width of the phase change material pattern 50 must be reduced. However, when the phase change material pattern 50 is formed using the photolithography process and the etching process as described above, there may be a limitation in reducing the size of the phase change material pattern 50. Accordingly, it may be difficult to form small phase change material patterns having a width less than about 100 nm using the conventional photolithography and etching processes. Further, if the width of the phase change material pattern 50 is greater than a width of the lower electrode 40, heat for changing the crystalline structure of the phase change material pattern 50 may be easily dissipated. Therefore, it is difficult to reduce power consumption, which is required to change the crystalline structure of the phase change material pattern 50.
Recently, another conventional method of fabricating phase change memory devices has been proposed to reduce the power consumption in a program mode. According to the other conventional method, an insulating layer is patterned to form an opening and a phase change material pattern is formed in the opening using a chemical vapor deposition (CVD) technique. However, when the phase change material pattern is formed in the opening using conventional CVD techniques, the phase change material pattern may be non-uniformly formed within the opening.